creating a microclimate box for metal storage

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Creating A Microclimate Box for Metal Storage

Number 4/16September 2011 Conserve O Gram

Introduction

Metal objects corrode and deteriorate whenexposed to moisture and pollutants. Iron andcopper alloy objects are especially vulnerableand can exhibit active corrosion reactions.Tese can develop rapidly and degrade an

object. o slow the process o deterioration( Museum Handbook 4:14; O:4; 5), house metalobjects below 35% relative humidity (RH).Metal objects, including those that are actively corroding, can be stabilized in a dry microcli-mate. Tis Conserve O Gram (COG ) providesguidance on how to create a microclimate stor-age box.

A microenvironment is an enclosed space withan airtight seal that controls RH with desic-cants such as silica gel (See “Using Silica Gel inMicroenvironments,” COG 1/8) or montmo-rillonite clay. Tese remove excess RH romthe enclosed space. A dry microenvironmentcan help stabilize actively corroding metalsand protect metal objects rom exposure tohigh RH. Tis storage solution also provideslocalized passive environmental control or allmetal objects by reducing risk o exposure toRH spikes. Because it does not use complex

mechanical systems, it is a low cost way to iso-late metals in a dry climate within a larger envi-ronment. Microclimate boxes can be readily set up within a storage area that houses othermaterials with dierent RH requirements.

Note: Do not use a dry microclimate storagebox or objects made o other materials such

as wood, glass and leather or composite objectsthat include metal.

Materials

• Polypropylene(PP) or Polyethylene (PE)storage container with silicon gasket

• Desiccant conditioned to 0-10% RH• Humidity indicator that reads 0-15% RH• pH neutral (archival) storage materials to

support object (archival corrugated board,polyethylene oam, twill tape, zipper lock bags)

Procedures

Prepare objects or storage in the microclimate

box:• Bag small objects in zipper lock bags

padded with polyethylene sheets.• Place larger objects on a tray and secure

with polyethylene oam bumpers or cottontwill tape ties. See Figure 1.

Figure 1. Metal objects prepared or storage in a tray andzipperlock bags.



2 Creating a Microclimate Box for Metal Storage

Conserve O Gram 4/16 National Park Service

Prepare the microclimate box:• Select polypropylene or polyethylene con-

tainer with silicon gaskets to accommodatethe objects and desiccant containers.

• Add the humidity indicatory card and posi-tion so the card can be read through thesidewall o the box.

• Prepare the appropriate quantity o desic-cant or the size o the container. (See COG 1/8). See able 1 or recommended quanti-ties o desiccant.

• Pack silica gel in permeable boxes or inresealable abric or yvek bags. (Notethat the yvek bag itsel cannot bereconditioned; the silica gel will need tobe removed or reconditioning.) Do not allow silica gel to come in direct contact with the objects.

• Place desiccant containers along the side oron the bottom o the box.

• Place the object(s) in the box. Ensure allcomponents are secure and do not all ontoeach other when moved. See Figure 2 tosee examples o components placed insidethe box.

Maintenance

Te polyethylene or polypropylene storagecontainer with a silicon gasket is moisturepermeable and humidity slowly leaks throughthe seal over time. Te desiccant will absorbthat moisture and regulate the environment orseveral years. However, the eectiveness drops with time. Te amount o time is dependenton the amount o moisture present in the localclimate. Te humidity indicator card providesa visual signal that the RH has increased

GeneralContainer Size

Volume

Quantity Recommended

Regular Density Silica Gel *

(18 kg/m3 or 1.1lb/ft3)


MontmorilloniteClay

(i.e. Desi –Pack*)(18 kg/m3 or 1.1

lb/ft3)


Rhapid Gel*(4 kg/m3 or0.25 lb/ft3)

4.75” x 11” x 4”8.5 cups/2 liters/ 2.1 quarts =122 in3 or 0 .07t3

1.5 ounces 1.5 ounces 0.4 ounces

9” x 11.5” x 3.5”16.5 cups/3.9 liters/4.1 quarts= 237.9 in3 or 0.14 t3 2.5 ounces 2.5 ounces 0.6 ounces

9” x 11.5” x 7.5”38 cups/9 liters/ 9.5 quarts =549 in3 or 0.32 t3 5.5 ounces 5.5 ounces 1.3 ounces

Table 1. Recommended Quantities of Desiccant for Sample Container Sizes.

*Silica gel amounts based on ‘Demystiying Silica Gel’ by Steve Weintraub.**Examples o desiccant available in today’s market, not recommendations o specifc products.

®®

Figure 2. Microclimate box components; box, desiccant,and humidity indicator.



3Creating a Microclimate Box for Metal Storage

National Park Service Conserve O Gram 4/16

beyond the desired level (See COG 14/12, ormore inormation on RH indicator cards).Monitor the microclimate environments on a quarterly basis. Te desiccant may need to bereconditioned or replaced on an annual basis.

Selected Sources:

Polypropylene (PP) or Polyethylene (PE) stor-age container with silicon gasket: grocery stores, large discount stores, and online atstores

Desiccant conditioned to 0-10% RH: Silica Gel Packets. www.silicagelpackets.com

Montmorillonite clay: Desi-Pak units. Sphinx Adsorbents, Inc. www.sphinxadsorbents.com/desipak.1.htm

RHapid GEL: Art Preservation Services. www.apsnyc.com

Hydrosorbent Compact Unit40 grams Silica Gel. Available through multiple

suppliers

Humidity Indicator Cards (5, 10, 15%):ULINE. www.uline.com

Archival storage materials to support objects:

archival corrugated board, polyethylene oam,twill tape, zipper lock bags: suppliers o library,museum and conservation materials.

Bibliography

Selwyn, Lyndsie. Metals and Corrosion: AHandbook for the Conservation Professional. Ottawa: Canadian Conservation Institute:2004

Tomson, Garry. Te Museum Environment ,2d ed. Oxord: Butterworth-Heinemann 1986

Voellinger, Teresa A and Sarah S. Wagner.“Cold Storage or Photograph Collections:Vapor Proo Packaging” Conserve O Gram 14/12, Washington, D.C: National Park Ser-vice, 2009

Weintrab, Steve. “Demystiying Silica Gel”

Objects Specialty Group Postprints (vol. 9), Washington, D.C: American Institute orConservation. 2002. [www.apsnyc.com/pd/silica_gel_SW_2003.pd]

Dana K. SengeConservatorNational Park ServiceIntermountain Region Museum Services Program255 N. Commerce Park Loopucson, AZ 85745

The Conserve O Gram series is published as a reference on collections

management and curatorial issues. Mention of a product, a manu-facturer, or a supplier by name in this publication does not consti-

tute an endorsement of that product or supplier by the National

Park Service. Sources named are not all inclusive. It is suggestedthat readers also seek alternative product and vendor information

in order to assess the full range of available supplies and equipment.

The series is distributed to all NPS units and is available to non-

NPS institutions and interested individuals on line at <http:// www.nps.gov/history/museum/publications/conserveogram/

cons_toc.html>. For further information and guidance con-

cerning any of the topics or procedures addressed in the series,contact NPS Park Museum Management Program, 1849 C

Street NW (2265), Washington, DC 20240; (202) 354-2000.

Figure 3. Microclimate boxes partially flled with objects.

creating a microclimate box for metal storage

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